(1) 1. Field of the Invention
The present invention relates to a method for promoting the drying of coatings which cure by oxidative polymerization and which contain drying or semi-drying oils. More particularly, the invention relates to a method for promoting drying of paints by incorporating therein 5-methyl-1,10-phenanthroline and to paint formulations containing 5-methyl-1,10-phenanthroline as a drier catalyst.
(2) Prior Art
It is well-known to those skilled in the paint art that unsubstituted o-phenanthroline, also known as 1,10-phenanthroline, is useful for promoting the drying of paints. Such a product is marketed under the trademark "ACTIV-8" by the R. T. Vanderbilt Company and is the subject of U.S. Pat. No. 2,565,897. Unfortunately, 1,10-phenanthroline has numerous disadvantages, one of which is that it is extremely costly to produce, making it undesirable for use in paints. More cost-effective alternatives which are better than unsubstituted 1,10-phenanthroline are required.
It was heretofore thought by those skilled in the coating art that 1,10-phenanthroline was unique in its action. The literature reports that of 400 compounds which are constitutionally related to it only one other compound.sup.1 was found to act similarly. Payne, H. F., Coating Technology, Vol. I, page 237 (1954). For a similar statement involving some 500 compounds see Stearns, M. E., 1,10-Phenanthroline Promotes the Drying of Paints, Official Digest, Chicago Paint and Varnish Production Club, September, 1954. FNT 1. See U.S. Patent 2,526,718 describing the use of .alpha.,.alpha.,-dipyridyl.
A number of substituted 1,10-phenanthrolines have been shown to be substantially less effective as paint drier catalysts than 1,10-phenanthroline itself. For example, both 2,5,9-trimethyl-1,10-phenanthroline and 2,9-dimethyl-1,10-phenanthroline are both quite inferior to the unsubstituted counterpart. We have now found, however, that 5-methyl-1,10-phenanthroline, is a highly effective drier catalyst for coatings containing drying and semi-drying oils and particularly for those containing manganese or cobalt paint driers. It is less costly to produce than 1,10-phenanthroline, is superior at comparable use levels in improving Surface and Hard Dry Times, is more effective in promoting low temperature drying of paints, and is superior to 1,10-phenanthroline in its ability to promote drying after prolonged storage of the formulated paint.